Haha, really I never touched it, should it be 1.0? I don't even know what it does.

Only GPS data has an absolute time stamp. If each video frame had an absolute time stamp, you wouldn't need to align the video with the data. It would be automatic. The sensor delays and the Video Synchronization represent the best approximation of the time difference between the GPS data and sensor and video data. If you loaded the data into a spreadsheet and compared the calculated acceleration curve with the measured curve, you could fine tune the offset. Unless you do that, it's difficult to tell the difference if you're only off a tenth or two. And it probably doesn't matter anyway for most people.

Harry, correct me if I'm wrong, but if you manually align the video using the finish line crossing, the video synchronization should be set to zero, as the alignment process takes care of the offset.

The Overlay Synchronization / Video delay is applied for every overlaying process and should not be used to adjust an individual video. It is the default setting for automatically triggered videos. I need to check the code but LapTimer should actually subtract the delay from the sync point set by the user manually - because it is added during overlay later. But I believe we are pretty off topic for this thread